Contact hypersensitivity to methyl red in female BALB/c mice.

Methyl red is a commonly used azo dye in laboratory assays, textiles, and other commercial products but little is known about its sensitization properties in humans. These studies were conducted to evaluate the sensitizing potential of methyl red using murine models of hypersensitivity. For the local lymph node assay, female BALB/c mice were dosed for 3 days with vehicle (dimethyl sulfoxide), positive control, or increasing concentrations (0.05-25%) of methyl red (CAS # 845-10-3) on the dorsal surface of each ear. Following injection of [3H] thymidine, draining lymph nodes were radioassayed on day 6. In the phenotypic analysis assay, mice were similarly exposed for 4 days. On day 10 post-exposure, serum was collected for total serum IgE analysis and lymph nodes were excised to evaluate B220+ and IgE + B220+ cell populations. Exposure to methyl red resulted in a dose dependent increase in lymphocyte proliferation reaching statistical significance (P < 0.05) at 0.5% and a calculated EC3 value (concentration required to induce a significant response) of 50 [micro]g/c[m.sup.2]. Phenotypic analysis demonstrated a significant increase in lymph node B220 + cells (P < 0.01), further supporting the potential for methyl red to induce sensitization. No change in serum IgE levels was observed following exposure to methyl red. These studies suggest the potential for methyl red to induce contact sensitization in humans.

Benjamin B, Hayes, MD, PhD, Shahla Azadi, MD, Ryan Sullivan, MD, Barbara J. Meade, DVM, PhD, and Mukta Panda, MD. Department of Medicine, University of Tennessee College of Medicine--Chattanooga Unit. Chattanooga, TN. National Institute for Occupational Safety and Health, Morgantown, WV.